Continuous method for mining trona



July 15, 1969 w. G. FlSCHER ET AL 3,455,606

CONTINUOUS METHOD FOR MINING TRONA Filed Jan. 31, 1968 2 Sheets-Sheet 1 r :1 OPERATOR/ Y I VI IV/HRS WILLIAM G. FISCHER JOHN D. NORGORD By JACK WILSON July 15, 1969 w FlSCHER ET AL 3,455,606

CONTINUOUS METHOD FOR MINING TRONA Filed Jan. 51, 1968 2 Sheets-Sheet 2 l\'\/'Y\'/'!)l WILLIAM G FISCHER JOHN D. NORGORD [H JACK WILSON nited States Patent 3,455,606 CONTINUOUS METHOD FOR MINING TRONA William G. Fischer, John D. Norgord, and Jack Wilson, Green River, Wyo., assignors, by mesne assignments, to Intermountain Research and Development Corporation, Cheyenne, Wyo., a corporation of Wyoming Filed Jan. 31, 1968, Ser. No. 702,057 Int. Cl. E21c 37/00, 45/00, 41/00 U.S. Cl. 299-11 4 Claims ABSTRACT OF THE DISCLOSURE In the mining of a horizontal bed of trona located between earth formations that are not as strong as the trona, a series of parallel lifts are cut through a pillar of trona, leaving fenders of trona which support the ceiling during mining and which avoid or minimize the need for ceiling bolts to support the mine roof.

BACKGROUND OF THE INVENTION Field of the invention The invention relates to the method of mining trona mineral by an improved mining technique which leaves fenders of trona to support the roof.

Description of the prior art Trona mineral, having the formula Na CO NaHCO is presently mined in the United States from trona deposits located in southwestern Wyoming. The underground deposits are in the form of horizontally extending beds having a thickness of from about 7 to about 13 feet located at a depth of from about 900 to about 1,800 feet below the ground. A trona bed normally lies between two horizontally extending strata of shale. Both the overlying and the underlying strata of shale have compression strengths on the order of about 3,400 p.s.i. and are substantially weaker than the trona bed, per se, which has a compression strength of about 7,500 p.s.i. Because the surrounding formations are weaker than the trona bed, per se, special techniques have been devised for mining trona to prevent caving of the roof and buckling of the floor into the mining cavity.

One technique commonly used in mining trona is the room and pillar mining system. In this system, essentialy rectangular tunels are cut in the trona formation; these are termed secondary entries. Substantially parallel rooms which are about 15 feet wide spaced about 50 to 60 feet apart are driven into the bed from the secondary entries using a continuous mining machine. The pillars of trona which remain between the rooms are then extracted by driving tunnels, called lifts, through the pillars. The lifts are separated from the mined out area by narrow fender (wall) of trona on the order of feet thick or less. When the lift is completed, the fender is removed by blasting, and the resulting unsupported roof adjacent the previously mined out area is caved. Prior to caving, the roofs of all entries, rooms and lifts are supported by roof bolts, preferably on font-foot centers, which are removed as much as possible before caving. This sequence is repeated, and upon completion of one lift the fender is blasted, and the next parallel lift is begun.

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One refinement in this technique which has beeen developed is that described in US. Patent 3,097,830, issued to Robert F. Love et al. on July 16, 1963. In this technique a first room is driven between a second room used for mining a pillar of trona and the still unmined areas; the first room is then deliberately collapsed next to the second room in which mining is to be conducted. In this way, pressure over limited areas to be mined is relieved.

Another refinement in the above room and pillar mining method is set forth in US. Patent 3,111,306, issued to Robert F. Love et al. on Nov. 19, 1963. In this mining method, lifts are driven in substantially a straight line through a tier of trona pillars to reduce the amount of turning or tramming that is necesary in using the continuous mining machine.

Whie the above patented processes are material improvements in the conventional room and pillar technique for mining trona, it stil does not solve the basic problem of relieving the pressure over the mined areas of the trona bed. As a result, the installation of room bolts is required to support the ceiling of rooms and lifts during mining; thereafter, the bolts are removed as much as possible prior to blasting the fenders and completely collapsing designated portions of the mined out area to relieve the overburden pressure. This blasting of fenders is most undesirable because caving of the roof takes place all at once, requiring carefully supervised blasting techniques, and introduces additional hazards, since the extent of caving is sometimes difiicult to control.

OBJECTS OF THE INVENTION It is an object of the present invention to provide for the continuous mining of trona by a process which eliminates the need for blasting of fenders and rapid caving of mined out areas.

It is anoother object of the present invention to provide a method for the continuous mining of trona wherein the use of roof bolts to support the roof and overburden can be substantially reduced or eliminated in the pillar being extracted.

It is a further object of the present invention to provide for the continous mining of trona in which a continuous mining machine can be employed and in which turning of the machine from one mining face to another can be substantially eliminated.

It is a still further object of the invention to provide for the continuous mining of trona by a continuous mining machine in which the machine operator always is on the Weak side (the side away from the main trona pillar), this weak side providing greater protection to the machine operator.

SUMMARY OF THE INVENTION A method of mining trona has been found comprising driving substantially parallel entries into a trona formation, connecting the entries by at least one primary passage, thus defining a main trona pillar to 'be mined located between the entries and the primary passage, driving a room through the main trona pillar, thereby forming a secondary pillar adjacent the main pillar, driving a lift from the room through the secondary pillar using a continuous mining machine, withdrawing the mining machine backwards through the lift into the room, driving another lift through the secondary pillar adjacent to the first lift and substantially parallel thereto and leaving a fender of trona separating the lifts, and continuing to drive lifts through the secondary pillar, leaving a plurality of substantially parallel fenders of trona remaining to support the roof of the mine. The lifts are driven by the conttinuous mining machine so that the remaining, unmined portions of the secondary pillar are on the same side (normally the left side) of the continuous mining machine, while the machine operator is on the opposite side (normally the right side), thereby affording him maximum safety and protection.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIGURE 1 is a plan view of a mine level illustrating the application of the present invention;

FIGURE 2 illustrates the mine level as mining is commenced by driving a double pass room through the entire width of the panel;

FIGURE 3 illustrates the extraction of a trona pillar as mining progresses;

FIGURE 4 illustrates the mine level after a number of double pass rooms have been cut and a number of pillars have been extracted.

DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS The present invention utilizes a mining technique in which rooms, preferably of double width, are cut through a trona panel, and the resulting pillar is extracted by cutting lifts through the pillar. The term rooms is used herein to denote the initial cuts made into a trona pillar and which connect entries together, While lifts are the tunnels cut through the pillars to remove the trona ore. The lifts are cut through by means of a continuous mining machine in which the operator is always on the weak side (the side opposite the remaining, unmined pillar). This is achieved by cutting a lift completely through a pillar, backing up the continuous mining machine through the lift to the original room from whence the machine started, and then cutting another lift parallel to the previous lift already cut. The lifts are driven with the machine operator on the weak side because the solid side (the side where the remaining pillar is left) sometimes builds up high shear stresses which cause the corner rocks to roll out from the wall. By maintaining the machine operator on the weak side at all times, greater safety is insured.

In driving these lifts through the pillar, a narrow fender (wall) of trona, perhaps as little as three feet thick, is left between the lifts to support the ceiling. Because the lifts are relatively short in length, and because of the remaining fenders of trona that act as supports, ceiling bolts are not needed within the lifts to support the mine roof.

Referring now to the drawings which illustrate a preferred embodiment of the practice of the invention:

In FIGURE 1 a series of entries 1A, 1B, 1C, 1D and 1B are joined together by passage 2 connecting the entries together. The entries and the passages are preferably cut using a continuous miner such as described in US. Patent 3,111,306, issued to Robert F. Love et al. on Nov. 19, 1963. The mining operation then begins as illustrated in FIGURE 2.

As shown in FIGURE 2, an initial, double pass room 4 is cut through the pillar connecting passages 1B and 1C. This is done by initially cutting a single pass room, normally about 14 feet Wide and 8 feet high the full width of the panel. Thereafter, a second pass is made, and in the second pass the width of the room is expanded to about 21 feet so that the ovaloidal walls cut by the continuous miner overlap to remove most of the bump formed in the roof. After room 4 has been cut, mining of pillar 20, bordered by passage 2 and room 4 is commenced, as shown in FIGURE 3.

As illustrated in FIGURE 3, the continuous mining machine commences in room 4 and cuts an initial lift 2A into pillar 20. When the lift has been completely cut through to passageway 2 (and partially passageway 1C), the mining machine is put in reverse and retraccs its path through the lift back into room 4. The continuous mining machine is then used to cut a second lift 2B through pillar 20 parallel to the first lift 2A such that a fender of trona 3A remains between lift 2A and 2B. This fender can be relatively thin, perhaps as little as three feet thick. Again, the continuous mining machine is put in reverse and backed out. of lift 2B into room 4 where it again is used to cut another lift 2C, leaving fender 3B between lift 2C and 2B. The same pattern is continued until all of pillar 20 has been extracted, leaving fenders 3A, 3B, 3C, etc. remaining. As will be seen from the drawing, the lifts are cut diagonally through pillar 20 in order to facilitate the continuous miner backing out of the lifts and into room 4 so that additional lifts can be cut through the pillar 20. It should be noted that during the cutting of the lifts the operator of the mining machine always sits on the weak side (the side opposite the remaining pillar 20) for the maximum safety.

In FIGURE 4 the entire operation of FIGURE 3 is repeated and additional rooms 6, 8, 10, 12 and 14 have been cut, and the pillars lying between rooms 40, 60, 80, and have been extracted in substantially the same way as set forth in FIGURE 3, leaving fenders of trona remaining between the room, e.g., 3A to 31 in pillar 20.

Ventilation of the working areas is carried out by passing air through entries 1A and 1B, through passages 2 and rooms 4, 6, 8 etc., and returning the air through passages 1C, 1D and 1E. Ventilation during mining is positively controlled because the dust travels from the head of the machine into a return air path with a minimum of contact with the working men. The movement of machines, supplies and personnel, and the removal of trona are accomplished through the entries. A belt conveyor 22 is normally employed to remove trona and is situated along a substantial length of one of the entries 1A.

The present process has many advantages over conventional room and pillar mining systems. Initially, roof bolting is not necessary within the pillar lift itself; thus both the cost of installing the roof bolts and the cost of the roof bolts, per se, are eliminated. Further, it is not necessary to turn the continuous miner around after completing a mining pass. This has always been difficult because of the bulk of the machine and the cramped working quarters. The safety of the machine operator is also improved by having him always on the weak side during the pillar extraction.

Another most important advantage of the present process is eliminating the need to blast trona fenders to produce controlled cavings. As a result high productivity is obtained because the continuous miner is in constant operation without tramming from one working place to the next, and without delays due to the required blasting. Another advantage of the present process is that after an entire block of ore has been mined out, the older fenders begin to slowly crush out and gradually lower the roof of the mine in a cantilever fashion. This causes the roof in a double pass room to be in compression and prevents it from developing tension cracks and local roof cavings experienced by other methods where Wide spans have been attempted.

What is claimed is:

1. A method of mining trona which comprises driving substantially parallel entries into a trona formation and connecting said entries by at least one primary passage, thereby defining a main trona pillar to be mined located between said entries and said passage, driving a room through said main trona pillar and forming a secondary pillar adjacent said main pillar, driving an initial lift from said room through said secondary pillar with continuous mining means, without drawing said continuous mining means back through said initial lift into said room, driving a second lift through said secondary pillar substantially parallel to said initial lift and leaving a fender of trona between said initial and said second lift, and continuing to drive lifts through said secondary pillar, leaving a plurality of substantially parallel fenders of trona remaining to support the roof of the mine.

2. Process of claim 1 wherein the lifts are driven diagonally through said secondary pillar.

3. Process of claim 1 wherein the continuous mining means always drives the lifts so that the remaining, unmined portion of the secondary pillar is always on the same side of the continuous mining means.

4. Process of claim 1 wherein said fenders of trona support said ceiling without using ceiling support members fixed into the roof of said mine.

References Cited UNITED STATES PATENTS OTHER REFERENCES Continuous Mining, Coal Age, July 1959, pages 212- 221 inc. (copy in group 350).

ERNEST R. PURSER, Primary Examiner US. Cl. X.R. 299-19 22333 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5, 55,606 Dated Jul 15, 1969 Inventor(s) William G. Fischer, John D. Norgor-d and Jack Wilson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 49, "tunels" should be "tunnels" Column 2, line 1, "beeen" should be "been" Column 2, line 18, "stil" should be "still" Column 2, line 36, "anoother' should be "another" Column 3, lines 4 and 5, "con-ttinuous" should be "continuous".

Column line 22., "for the maximum" should be "for maximum Column 5, line 1, without drawing should be "withdrawing" SIGNED AND SEALED AUG 1 149m Amt:

Edna-GEM!!- mm 3, 3.

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